sum up arthurs reaction to the green knights visit

Arthur's reaction is one of excitement and elation but, at the same time, he must remain "kingly",

"Wanderer, know you are welcome here.

dismount, if you may; make merry as you wish,

and we may learn in a little while what you would like."

At first no one will take the Green Knight on his challenge. The Green Knight mocks them, Arthur in particular. Arthur can't look like a coward here so he jumps up,

Wanderer, know you are welcome here.

dismount, if you may; make merry as you wish,

and we may learn in a little while what you would like."

"Look here, by heaven! Have you lost your mind?

If you want to be mad, I will make you welcome!

Nobody I know is bowled over by your big words,

so help me God! Hand me that ax --

I will grant you the gift you beg me to give!"

The scene sets us up for an incredible adventure. While the knights are in shock the king shows that he is not afraid of a challenge (when publicly mocked).He, at least, has the appearance of a soldier and leader.